1. Field of the Invention
The present invention relates to a speed control circuit for a DC motor, and in particular to a speed control circuit for a DC motor utilized to operate movable elements in a communications terminal.
2. Description of the Prior Art
The use of DC motors for drive purposes in terminals in communications technology is known in the art. Such motors may be used, for example, to position platens, printer carriages, and type wheels.
A speed control circuit for a DC motor is described in the text "Theory and Applications Of Phase Locked Loops," Best, Second Edition, page 93. In this circuit, the DC motor, in combinaton with a pulse transmitter and a voltage controlled regulator for the motor current, functions essentially as a voltage controlled oscillator. One side of the DC motor is connected to ground. This conventional circuit has the disadvantage that because deceleration is produced only by friction and the electromotive force, speed fluctuations, in particular fluctuations occurring at low speeds, can only be slowly adjusted.